Imprint lithography (also referred to as soft lithography) is a promising technique for transferring images from an imprint stamp to a media in which the images are replicated. Unlike current state-of-the-art photolithographic processes which require very expensive process equipment to make masks and to expose a photoresist material with an image on the mask, imprint lithography is a low cost process that eliminates the expensive mask making equipment and lithographic equipment, not to mention the equipment and materials needed to develop and etch the photoresist material. Nano-imprint lithography is a promising technique for obtaining nano-size patterns (as small as a few tens of nanometers or less) in a media. A key step in forming the nano-size patterns in the media is to first form an imprint stamp that includes a pattern that complements the nano-sized patterns that are to be imprinted in the media. Although an imprint stamp can be made to imprint features of any size, imprint stamps with features that are nanometer sized or smaller are of particular interest because of a need to imprint features that are smaller than a lithography limit of current optical base photolithography processes and at a lower cost.
In FIG. 1a, a prior nano-imprint lithography process includes an imprint stamp 200 having a plurality of imprint patterns 202 formed thereon. In FIG. 1b, the imprint patterns 202 consists of a simple line and space pattern having a plurality of lines 204 separate by a plurality of spaces 206 between adjacent lines 204. In FIG. 1a, by pressing (see dashed arrow 201) the imprint stamp 200 onto a mask layer 203, a thickness of the mask layer 203 is modulated with respect to the imprint patterns 202 such that the imprint patterns 202 are replicated in the mask layer 203. Typically, the mask layer 203 is made from a material such as a polymer. For example, a photoresist material can be used for the mask layer 203. The mask layer 203 is deposited on a supporting substrate 205. Using a step and repeat process, the imprint stamp 200 is repeatedly pressed 201 into the mask layer 203 to replicate the imprint patterns 202 in the mask layer 203 and to cover a desired area of the mask layer 203.
In FIG. 2, after the step and repeat process, the mask layer 203 includes a plurality of nano-size impressions 207 that complement the shape of the imprint patterns 202. In FIG. 3, the mask layer 203 is anisotropically etched (i.e. a highly directional etch) to form nano-sized patterns 209 in the mask layer 203. Typically, the supporting substrate 205 or another layer (not shown) positioned between the mask layer 203 and the supporting substrate 205 serves as an etch stop for the anisotropic etch. Alternatively, the mask layer 203 can serve as an etch mask for an underlying layer (see reference numeral 208 in FIGS. 7a through 7d) and the pattern of the nano-size impressions 207 is replicated in the underlayer 208 by a subsequent anisotropic etch process.
In FIG. 4a, the formation of the imprint patterns 202 on the prior imprint stamp 200 begins by depositing alternating layers of thin film material (211, 213) on a substrate 215 to form a multi-stacked thin film 210 that extends outward of a surface 215s of the substrate 215. In FIG. 4b, the thin film layers (211, 213) have thicknesses tA and tB respectively that can be the same or that can vary. For example, the layer 211 can have a thickness tA that is thicker at one level of the multi-stacked thin film 210 and thinner at another level of the multi-stacked thin film 210 as depicted in FIG. 4b. Similarly, the layer 213 also has thicknesses tB that vary in thickness in the multi-stacked thin film 210. Those variations in thickness (tA, tB) will result in variations in the simple line and space patterns (204, 206) in the imprint pattern 202 of the imprint stamp 200 as will be described below in reference to FIGS. 5a through 5c. 
In FIG. 4a, the multi-stacked thin film 210 is then sliced into a plurality of discrete segments Δs along a direction shown by dashed arrow S. For example, in FIG. 4c, the substrate 215 can be a wafer of semiconductor material upon which the multi-stacked thin film 210 is deposited. After all layers of the multi-stacked thin film 210 have been deposited, the wafer (i.e. the substrate 215) is then sliced, using a saw or the like, to form the discrete segments Δs.
In FIG. 5a, a discrete segment Δs includes a portion of the multi-stacked thin film 210 and a portion of the substrate 215. In FIGS. 5b and 5c, the discrete segment Δs is selectively etched to define the imprint pattern 202. Differences in etch rates between the alternating layers (211, 213) causes one of the layers to be etched at a faster rate than the other layer and results in differences in height between the alternating layers (211, 213). Those differences in height define the imprint pattern 202. Additionally, the differences in the thicknesses (tA, tB) determines the variations in the widths of the lines 204 and the widths of the spaces 206 of the imprint pattern 202. The imprint pattern 202 is formed on a portion IA of the imprint stamp 200 as illustrated in FIGS. 5b, 5c, and 6. A remaining portion NA of the imprint stamp 200 is a non-patternable area, that is, the portion NA cannot be used for imprinting because that portion of the substrate 215 does not include an imprint pattern.
One disadvantage of the prior imprint stamp 200 is the imprint pattern 202 consists of simple line and space patterns (204, 206) as depicted in FIGS. 6, 7a, 7b, 7c, and 7d, wherein, the line and space patterns (204, 206) are substantially parallel to each other as denoted by dashed lines P in FIG. 7a. Consequently, in FIGS. 7b, 7c, and 7d, the resulting nano-size impressions 207 are also limited to simple line 204′ and space 206′ patterns because they complement the line and space patterns (204, 206) of the imprint pattern 202 and are therefore also substantially parallel to each other as denoted by dashed lines P in FIGS. 7b and 7c. 
In FIG. 7a, the imprint stamp 200 is pressed 201 onto the mask layer 203 to replicate the simple line 204 and space 206 patterns of the imprint pattern 202 in the mask layer 203. In FIG. 7b, after the pressing step, the mask layer 203 includes the complementary nano-size impressions 207 replicated therein. As was noted above, the nano-size impressions 207 also have the simple line and space pattern denoted as 204′ and 206′ respectively. In FIG. 7c, the mask layer 203 is anisotropically etched until the space patterns 206′ are coincident with an upper surface 208′ of an underlayer 208 and the line patterns 204′ extend outward of the upper surface 208′. The line and space patterns (204′, 206′) will serve as an etch mask for a subsequent anisotropic etch step. Next, in FIG. 7d, the underlayer 208 is anisotropically etched through the mask created by the line and space patterns (204′, 206′) to define the nano-size patterns 209 that complement the simple line and space patterns (204, 206) of the imprint stamp 200. The nano-size patterns 209 occupy a patterned area PA of the substrate 205; whereas, a remainder of the substrate 205 comprises an unpatterned area UA.
Consequently, there exists a need for an imprint stamp that includes an application specific imprint pattern comprising complex patterns and shapes. There is also a need for an imprint stamp that includes an application specific imprint pattern that includes feature sizes that are smaller than a minimum resolution of a lithography system used in fabricating the imprint stamp. Furthermore, there is a need for an imprint stamp that includes an application specific imprint pattern that includes feature sizes that are of nanometer dimensions or less.